Lens displacement detection circuit for an optical device

Abstract

A lens is positioned to be received by a lens holder. The lens includes a first electrical trace and the lens holder includes a second electrical trace. The first and second electrical traces form electrodes of a sense capacitor. A capacitance of the sense capacitor is sensed. From the sensed capacitance, a determination is made as to whether the lens is present and properly positioned in the lens holder.

The invention claimed is: 
     
       1. An optical device, comprising:
 a lens holder; 
 a lens; 
 wherein the lens holder is configured to receive the lens; 
 wherein the lens includes a first electrical trace; 
 wherein the lens holder includes a second electrical trace; and 
 wherein the first and second electrical traces form electrodes of a sense capacitor; 
 a capacitive sensing circuit electrically coupled to the first and second electrical traces and configured to sense a capacitance of the sense capacitor; and 
 a light emitting circuit configured to emit light that passes through said lens, and wherein said light emitting circuit is enabled for operation if the capacitance of the sense capacitor sensed by the capacitive sensing circuit is within a certain range. 
 
     
     
       2. The optical device of  claim 1 , wherein said capacitance of the sense capacitor is within the certain range when the lens is present and properly positioned in the lens holder. 
     
     
       3. The optical device of  claim 1 , wherein said first electrical trace forms a first closed loop. 
     
     
       4. The optical device of  claim 3 , wherein said second electrical trace forms a second closed loop, and wherein the first and second closed loops are concentric when the lens holder receives the lens. 
     
     
       5. The optical device of  claim 1 , wherein the first and second electrical traces extend parallel to each other. 
     
     
       6. An optical device, comprising:
 a lens holder; 
 a lens; 
 wherein the lens holder is configured to receive the lens; 
 wherein the lens includes a first electrical trace; 
 wherein the lens holder includes a second electrical trace; and 
 wherein the first and second electrical traces form electrodes of a sense capacitor; 
 a capacitive sensing circuit electrically coupled to the first and second electrical traces and configured to sense a capacitance of the sense capacitor; and 
 a light emitting circuit configured to emit light that passes through said lens, and wherein said light emitting circuit is disabled for operation if the capacitance of the sense capacitor sensed by the capacitive sensing circuit is outside a certain range. 
 
     
     
       7. The optical device of  claim 6 , wherein said capacitance of the sense capacitor is outside the certain range when the lens is not present in the lens holder. 
     
     
       8. The optical device of  claim 6 , wherein said capacitance of the sense capacitor is outside the certain range when the lens is not properly positioned in the lens holder. 
     
     
       9. The optical device of  claim 6 , wherein said first electrical trace forms a first closed loop. 
     
     
       10. The optical device of  claim 9 , wherein said second electrical trace forms a second closed loop, and wherein the first and second closed loops are concentric when the lens holder receives the lens. 
     
     
       11. The optical device of  claim 6 , wherein the first and second electrical traces extend parallel to each other. 
     
     
       12. A method, comprising:
 positioning a lens to be received by a lens holder; 
 wherein the lens includes a first electrical trace; 
 wherein the lens holder includes a second electrical trace; 
 wherein the first and second electrical traces form electrodes of a sense capacitor; 
 sensing a capacitance of the sense capacitor; 
 determining from the sensed capacitance whether the lens is present and properly positioned in the lens holder; and 
 enabling a light emitting circuit for operation if the sensed capacitance of the sense capacitor is within a certain range. 
 
     
     
       13. A method, comprising:
 positioning a lens to be received by a lens holder; 
 wherein the lens includes a first electrical trace; 
 wherein the lens holder includes a second electrical trace; 
 wherein the first and second electrical traces form electrodes of a sense capacitor; 
 sensing a capacitance of the sense capacitor; 
 determining from the sensed capacitance whether the lens is present and properly positioned in the lens holder; and 
 disabling a light emitting circuit for operation if the sensed capacitance of the sense capacitor is outside a certain range. 
 
     
     
       14. The method of  claim 13 , wherein said first electrical trace forms a first closed loop and wherein said second electrical trace forms a second closed loop, and wherein positioning the lens comprises arranging the first and second closed loops to be concentric. 
     
     
       15. The method of  claim 13 , wherein sensing the capacitance comprises:
 applying a periodic charging to sense capacitor; and 
 sensing a voltage on said sense capacitor as a result of said periodic charging. 
 
     
     
       16. The method of  claim 15 , wherein sensing the voltage comprises comparing the voltage on said sense capacitor to a threshold and generating a periodic output signal having a pulse width that is indicative of the capacitance. 
     
     
       17. The method of  claim 12 , wherein said first electrical trace forms a first closed loop and wherein said second electrical trace forms a second closed loop, and wherein positioning the lens comprises arranging the first and second closed loops to be concentric. 
     
     
       18. The method of  claim 12 , wherein sensing the capacitance comprises:
 applying a periodic charging to sense capacitor; and 
 sensing a voltage on said sense capacitor as a result of said periodic charging. 
 
     
     
       19. The method of  claim 18 , wherein sensing the voltage comprises comparing the voltage on said sense capacitor to a threshold and generating a periodic output signal having a pulse width that is indicative of the capacitance. 
     
     
       20. An optical device, comprising:
 a lens holder; 
 a lens; 
 wherein the lens holder is configured to receive the lens; 
 wherein the lens includes a first electrical trace; 
 wherein the lens holder includes a second electrical trace; and 
 wherein the first and second electrical traces form electrodes of a sense capacitor; 
 wherein said first electrical trace forms a first closed loop; 
 wherein said second electrical trace forms a second closed loop; and 
 wherein the first and second closed loops are concentric when the lens holder receives the lens. 
 
     
     
       21. The optical device of  claim 20 , wherein the first and second electrical traces extend parallel to each other. 
     
     
       22. The optical device of  claim 20 , further comprising:
 a circuit configured to sense a capacitance of the first and second closed loops; and 
 a light emitting circuit configured to emit light that passes through said lens, and wherein said light emitting circuit is enabled for operation if the sensed capacitance is within a certain range. 
 
     
     
       23. The optical device of  claim 20 , further comprising:
 a circuit configured to sense a capacitance of the first and second closed loops; and 
 a light emitting circuit configured to emit light that passes through said lens, and wherein said light emitting circuit is disabled for operation if the sensed capacitance is outside a certain range.